The problem of component damage during the actual operation of the electronic belt scale often troubles the on-site maintenance personnel. Because there are no spare parts, the electronic belt scale often results in outage.
01
When visiting a mineral processing plant, I saw that a belt scale has been out of service. This scale is a BMP double-roller electronic belt scale from the German Schenck company introduced by the original Chengdu Scientific Instrument Factory. It is from the crushing workshop to the grinding The transfer point of materials in the floating workshop, so it is a key measurement point. After asking the reason, I found out that the speed sensor was damaged, and the spare parts could not be bought, so I had no choice but to use them. Although I have not debugged the secondary instrument of this kind of scale, I know that most of the secondary instruments have such a function, that is, the selection function of internal pulse and external pulse. When the external pulse is selected, it is installed on the belt conveyor The speed sensor provides pulse signals to the secondary instrument. When the internal pulse is selected, the signal pulse source in the secondary instrument will provide the pulse signal. That is to say, when the speed sensor is working normally, we can choose the external pulse mode, and the speed sensor installed on the belt conveyor will provide the pulse signal to the secondary instrument; when the speed sensor is damaged, we can choose the internal pulse mode, then by The signal pulse source inside the secondary instrument provides pulse signals.
02
I asked the on-site maintenance personnel of the electronic belt scale to power the secondary instrument that has been out of service for many years and call the menu. When it is adjusted to “Tacho. Active?” (the speed sensor is effective?), we can see that we can choose “yes” or “no” (here “yes” means that the speed sensor installed on the belt conveyor provides pulse signals to the secondary instrument, that is, the external pulse mode; “no” means that the signal pulse source in the secondary instrument provides pulse signals , that is, the internal pulse mode), when we change the selection from “yes” to “no”, and set the actual speed value in the next step of the menu “Nominal Speed” (rated speed), the upper left of the secondary instrument of the BMP belt scale The small light spot on the square starts to rotate again, indicating that there is a speed measurement signal, and the belt scale starts working again (please note that only when you know the various settings of the secondary instrument in advance, you know that the belt scale does not use speed measurement. sensor can also maintain operation).
03
But there is still a lot of inconvenience without a speed sensor. For example, when the belt conveyor stops running, the secondary instrument will jump slowly due to the remaining material on the belt or the uneven tare weight of the belt, resulting in the continuous accumulation of material without transporting materials. The problem. At that time, I happened to have a domestic speed sensor on hand, and wanted to use it to see if it could replace the original Schenck product. They are all pulse type, but Schenk’s products have two wires in the world, and domestic products have three wires, and the extra one is the power ground. Repeated tests, it is not enough to connect only two wires with domestic products, try to connect the third wire to the power input of the load cell (see picture). After connecting, the small light spot on the upper left of the secondary instrument of the belt scale starts to rotate again, indicating that the secondary instrument can receive the signal of the three-wire speed sensor at this time. ) column to modify the speed display value, the electronic belt scale works normally.
Use a three-wire speed sensor to replace the wiring of a two-wire speed sensor
04
After the scale resumed operation for a period of time, the secondary instrument began to fail frequently, and the on-site maintenance personnel asked to replace the secondary instrument. We analyzed the input signal of the original secondary instrument, it only has the mV signal of the load cell and the pulse signal of the speed sensor, which is exactly the same as the input signal of the domestic secondary instrument, so it is entirely possible to use a low-cost, good-performance Replacement of domestic secondary instruments. We chose the WPC-DII secondary instrument produced by Hunan Computer Factory, the speed sensor has restored the three-wire connection, the mV signal and power supply of the load cell are also connected as required, and the secondary instrument is working normally. But soon it was found that the scale displayed normal in the middle and low range, but in the high range, the display value of the meter no longer increased, as if the measured value was “clamped”. After inspection, the output of the load cell is normal in the high range, and the problem may appear in the secondary instrument. After consulting the manual, I learned that the mV signal input range of the WPC-DII secondary instrument is 20mV, and the output of the load cell is close to 20mV in the high range. 30mV, so there is a “clamping” phenomenon. This is a mistake caused by ignoring this indicator when we replaced the secondary instrument selection. The only way to make up for it is to add a drop-down resistor to the bridge supply voltage circuit of the load cell, so that the bridge supply voltage supplied to the load cell After the voltage is reduced by about 1/3, the “clamping” phenomenon no longer occurs.
05
The scale was stopped, restored, and then gradually started to work normally. In addition to replacing the speed sensor and the secondary instrument, we also felt that the original installation position was inappropriate, so we removed the scale frame, found a more appropriate position and reinstalled it. A verification method has been formulated to make this scale better as it is used.
